The invention relates to a method for testing and safeguarding the availability of a networked system. In particular, the method relates to safeguarding the availability of a networked system that is, inter alia, also connected with possible reference-earth potential displacements.
German patent document DE 42 12 742 A1 discloses a method for detecting errors in a data bus having two bus lines which are driven via output stages at least of one of the bus subscribers. Here, the possibility exists that the two output stages of a bus subscriber are driven simultaneously upon commissioning of the data bus. In this case, the ability to determine the level of the potential of a bus line and to generate an error report by the bus subscriber given a lack of agreement with a set point is provided.
U.S. Pat. No. 4,908,822 describes a multiplex system for addressing, controlling and monitoring the status of a multiplicity of electric devices which are distributed throughout a vehicle. A component of the multiplex system is two bus lines via which respectively identical messages are transmitted in series. In this case, the bus lines are each operated as single-wire buses which address a multiplicity of microcontrollers, each of the last of which respectively drives two control elements. Signals with a variable pulse duty factor can be impressed on the bus lines for test purposes, in order to thereby switch addressable control elements on and off. Switching means of the controllers provide current signals for representing the status of the element respectively driven.
Reference may be further made to German patent document DE 19611944 A1; WO97/36399; WO97/36398 and to patent application PCT/EP97/01534, which was submitted at the same time with the present application, the disclosures of which are expressly incorporated by reference herein.
In this case, German patent document DE 19611944 A1, describes an integrated semiconductor circuit with an electronic control unit having a microcontroller. Here, the control unit is able to communicate with other control units which are controlled by microcontrollers and for this purpose form a controller area network (CAN) in which communication is conducted on the basis of the protocol via a two-wire line. For this purpose each control unit has a bus protocol function.
According to the invention disclosed in DE 19611944A1, in the first embodiment, this circuit maximizes the availability of the CAN. This is accomplished because, on the one hand, it implements a transceive function which tolerates bus errors and also permits communication even in the presence of a bus error, and on the other hand it has means for detecting and treating bus errors, which in the case of an error isolates the bus from its normal subscriber terminations and reterminates it. As a result of this, while maintaining an ability to communicate, the circuit prevents (particularly in the case of very large CANs) parasitic currents from flowing away from subscribers via the bus into the bus error point in a bus-wide manner. The parasitic currents limit the availability of the network to the point of exhausting the battery in a battery-supported bus system. That circuit to this extent integrally increases the network availability on two levels, specifically on the level of communication and on the level of system energy. Another strategy, likewise for increasing the availability, is pursued by a different embodiment of that circuit.
WO97/36399 describes a method for determining potential displacements between electronic modules in a wire bus-type network, or the correspondence quality of their communication service levels in the network interconnection. Here, the bus medium comprises at least one wire which is connected electrically to the electronic modules. According to the invention disclosed in WO97/36399, an offset voltage is added in at least one bus subscriber (test subscriber) at the transmitting end to (at least) one (of the two) dominant, normal source level(s) and a test message is transmitted into the bus-type network by the test subscriber in this status. In this case, the source level is varied in a predetermined way. Depending on whether the (at least) one (of the two) dominant source level(s) is lowered or raised by the respectively adjustable offset voltage, the bus subscriber, which has a (reference-earth) potential error loses or gains its ability to receive. This condition is evaluated. Furthermore, WO97/36399 describes a device which comprises cooperative potential-controlling means hat are or can be connected to the transceiver function of a bus subscriber. Here, the device implements together with the controlling means, at least with respect to parts of the transmitting and/or receiving means of the transceiver function, at least one controllable voltage source which permits the exertion of an influence on at least one source level that is dominant during transmission and/or at least one signal level that is discriminant during reception.
WO97/36398 describes a semiconductor circuit for an electronic device which has at least one microcontroller. The circuit comprises at least one voltage regulator for providing, from a first supply voltage, at least one second supply voltage for the at least one microcontroller and for circuits of the device which cooperate with the microcontroller. Furthermore, as a monolith, this circuit comprises a transceiver function having transmitting and receiving means for coupling a microcontroller to a two-wire bus. According to a development of the invention disclosed in WO97/36398, this circuit further comprises watchdog functions, various wake-up functions and an interface via which serial data exchange is possible with the at least one microcontroller. Moreover, the circuit can have means for network-wide determination of bus subscribers with reference-earth potential errors and for quantifying such errors.
Various developments of these means in conjunction with special designs of the receiving part of the transceiver enable a bus-type network, for example of the CAN type, based on the circuit to make a latent determination (as the most important measure of the bus Q) of the margin of error still present in advance of the first occurrence of an operational failure caused by a level error.
PCT application PCT/EP97/01534 describes a method for testing the grounding of parts of a bus-networked system. In this case, steady-state potentials on bus lines are compared with reference-earth potentials which can be generated inside a bus subscriber. This comparison is used to infer (in each case) the quality of the interface between the bus subscriber under consideration and the earth reference conductor which is common throughout the network. A device for carrying out this method is also proposed herein.
Networked systems for control purposes which are based on a wire bus as means of communication are experiencing an increased importance. Examples are bus-type networks according to the J1850- or CAN-standard.
In such networked systems, a multiplicity of bus subscribers (these preferably being electronic controllers), of which each contains a microprocessor or a microcontroller, communicate with one another via a bus-type network. In the case of a CAN for example, the bus-type network comprises two conductor strands or wires which are normally keyed dominantly in phase opposition.
At the same time, there are also bus-type networks which use (as a bus medium) a single conductor strand or wire over an electric busbar or common surface. In these networks, though, the bus medium mostly serves as a power supply conductor. In this case, the subscribers communicate via the bus-type network via transmitting/receiving means (so-called bus transceivers). In each case, as an essential component of each bus subscriber, the so-called bus transceivers physically couple the latter to the bus-type network.
These transceivers for transmitting and receiving the data messages convert data messages from the logic level inside the relevant bus subscriber to signal levels on the bus wire or wires, and vice versa. With respect to different features (expedient within the scope of the present invention), of a suitable bus transceiver, explicit reference is made here to German patent document DE 19611944 A1 and WO97/36398.
With systems in an interference-critical environment, it is preferred to use two-wire bus-type networks in the interest of a high signal-to-interference ratio. This is because single-wire networks are more sensitive over a reference conductor surface to possible potential interference. In particular single wire networks are more sensitive to incoming and outgoing electro-magnetic interference. Furthermore, because of their (in this respect) limited radio-frequency electromagnetic compatibility (EMC), single-wire networks are preferably used in the case of relatively low data rates. Given a suitable design of their transceivers, such two-wire bus-type networks can also be operated (in an emergency) in the abovementioned single-wire operating mode, i.e., one of the two bus wires with respect to a reference-earth potential available in a network-wide fashion (if appropriate) with a lower data rate.
In such systems, normal communication takes place by keying in phase opposition of the two conductor strand potentials (in each case) from a recessive to a dominant single level, i.e., differentially. In the case of single-wire (emergency) operation or in single-wire networks, communication takes place (as a rule) by keying the single bus wire from a recessive to a dominant signal level with respect to the reference-earth potential bar or conductor surface. Data is transmitted in this case by virtue of the fact that different voltage levels are applied to the bus line(s). The data is determined by evaluating the corresponding voltage levels at the receiving end. If this is impaired in any way, depending on the effect, operational communication malfunctions are present which partially or completely nullify the availability of the networked system.
Consequently, in both the case of single-wire and two-wire bus systems, for example, the abovementioned signal levels are kept inside certain tolerance windows via special circuit measures. As a result, it is always possible for signals to be transmitted without interference between all the bus transceivers. In order to transmit data, a voltage level is applied to the bus wire at the transmitting end which is above or below a discrimination level. This discrimination level is defined as a threshold value in the receiving subscriber and must be overshot or undershot in order to enable detection of the presence of the abovementioned transmitting-end voltage level as a truth condition. As a result of this, in the case of certain, permissible deviations in a reference-earth potential between individual subscribers (in each case) it is still possible nevertheless for data to be exchanged between the subscribers.
In practice, to generate appropriate levels and tolerance windows, use is made of the fact that, for example, the microprocessor or microcontroller in each bus subscriber (in any case) requires an operating voltage which has to be to be kept within narrow limits. This operating voltage is derived, as a rule, from a primary potential via the voltage regulator which is also a component of the bus subscriber.
This relatively accurate operating voltage (internal to the subscriber) then determines the (one of the two) source level(s) dominant in the case of transmission, from which data are xe2x80x9ckeyed upxe2x80x9d, as it were, from the (respective) bus wire on a recessive level. Thus, for example, in a two-wire bus system according to the CAN standard, use is made of a dominant high level of, for example, 5 volts, that corresponds to a common supply voltage of 5 volts for integrated circuit functions which has to be kept constant in a relatively accurate manner in each bus subscriber in any case via electronic regulating means.
The transceivers are generally designed such that they still perform (in a manner free from error) the corresponding level conversions of the data messages. This is true even if the reference levels of the transceivers exhibit (with respect to one another) certain admissible potential differences which, respectively, do not exceed a maximum value.
Transmission problems occur in such systems, for example, when (for whatever reasons) the correspondence (within specified tolerance ranges) between the bus level(s), which is (are) set up in a dominant fashion in terms of transmission on the bus wire(s), and/or the effective discrimination level(s), tuned thereto in terms of reception, for evaluating the truth of signal edges or signal potentials when a bus-type network suffers or deteriorates to such an extent that the abovementioned maximum values are exceeded.
A similar statement holds analogously for network-wide malfunctioning of the recessive level window.
In a corresponding way, it is possible, for example, for signal overshooting, exceeding a certain limiting measure, on the bus bit shoulder, for example, because of terminating the bus line at subscribers in a fashion exhibiting discrepancies in wave impedance. It is also possible for signal rise times which are not (no longer) matched to one another to cause transmission problems which (when they coincide with problems based on fault potentials) can not only nullify the availability of a networked system, but can render difficult removal of the totality of faults.
For the purpose of the highest possible availability, two-wire bus-type networks and the transceivers used therein can preferably be constructed such that, for example, in the case of a short circuit of a bus wire (for example) with the reference-earth potential bar or reference-earth potential conductor surface, the abovementioned emergency communication is automatically rendered possible and instituted in the said single-wire operating mode via the other bus wire that is not affected by a fault.
In this case, however, the permissible faults or possible tolerance ranges, for example, for the recessive and/or dominant communication levels for single-wire (emergency) operation or in single-wire networks are then smaller or narrower, respectively, than in the case of differential two-wire (normal) operation.
The consequence of this can be that in the case where tolerance has already largely been exhausted for a communication level in the differential two-wire operation, when a short circuit then occurs of one of the two bus wires occurs, the level error (previously still permissible for the two-wire operation) on the bus wire not affected by the short circuit is already outside the tolerance range for permissible level errors in the single-wire (emergency) operation. As a result of this such an emergency operation can then be prevented.
The most important practical case of corresponding level disturbances are potential disturbances induced locally by subscribers. They occur when, for example, a supply potential of all the bus subscribers is drawn from a busbar or conductor surface of the system carrier which is used in a system-wide fashion, (i.e., spatially extended), but inside which a defective voltage drop occurs. Here, the result is that the affected supply potential (as seen from the bus medium) is no longer equal for all bus subscribers. The extended busbar or conductor surface has then (as seen from the bus medium) lost its function as a system-wide equipotential surface.
In the exemplary case of a controller in a transport means as system carrier, whose entire body is known to serve as distribution conductor surface (xe2x80x9cearthxe2x80x9d), such a thing can be due to a defective longitudinal voltage drop in this earthing surface. For example, due to a high fault current or else to a defective earth connection of a bus subscriber which, when the normal earthing current of the relevant subscriber is applied, leads to an excessively large local voltage drop. In that respect, it also leads to a rise in the reference-earth potential of the affected subscriber with respect to the earth potentials of the remaining subscribers in the bus-type network. As a result of this, such a subscriber can then, for example, no longer be addressed via the bus. This is because the discrimination level window of the receiver, not defective per se, of its bus transceiver appears to be raised by the absolute value of its earth base point fault voltage with respect to other subscribers, and is thus then too low in real terms in the subscriber for a communication.
It is clear from this practical example of interference caused by reference-earth potential errors that in the case of systems with very many subscribers the availability of the system, and to that extent the unlimited usability of a system carrier controlled by the system, for example a transport means, can be ensured only by safeguarding adequate separations of permissible limiting values of the bus level(s) set up on the bus wire(s), and/or of the effective discrimination level(s), adjusted thereto in terms of reception, for the truth evaluation of signal edges or signal status. Since, for example, potential errors in the earth path of controllers in transport means, for example, preferably develop in a creeping fashion owing to corrosion over time, intensely networked systems (with many subscribers) require an increased testing outlay by comparison with sparsely networked systems (with fewer subscribers) in order to be able to ensure availability or usability which is sufficiently reliable.
As for the signal levels, this also holds in a similar way for other transmission parameters subject to limiting values in a system-wide fashion such as, for example, the slew rate compliance, the overshoot damping measure, etc., which, in conjunction with adequate limiting value separations of the above-named signal levels, define a measure of the bus quality or network quality and which can be used to derive a variable that characterizes the reliability of the availability of the overall system.
It is therefore an object of the invention to provide a method for testing and safeguarding the availability of a networked system which minimizes the outlay to be made in order to ensure a reliable availability of the system.
This and other objects and advantages are achieved by the method according to the invention, by virtue of the fact that during operation of the system, signals present on the bus-type network are discriminated or tested or measured with respect to at least one signal criterion by individual subscribers under conditions defined in a network-wide fashion for all subscribers. Here, characteristic status data is generated (in each case) for each signal criterion with respect to each subscriber and is collected and arranged in at least one status map of the system. The status data characterizes both the current and at least one earlier status with regard to the tested subscribers with respect to the at least one criterion further, at least one measure of the margin of error of the networked system with respect to the at least one criterion is obtained from the status data.
As a result, it is possible to detect during normal system operation, but in any case on the occasion of maintenance of the system carrier, that is at the inspection intervals thereof, whether there was or is present in the system operation a measure of the margin of error of the system which is still adequate or no longer adequate with regard to the at least one criterion and, if appropriate, requires a preventative measure which continues to safeguard the availability of the system or in the case of latent impairment of an emergency operation restores the potential possibility of the emergency operation. Such an anticipatory serviceability, which is thus provided even before the first occurrence of a communication fault or communication defect, maximizes the availability of intensely networked and/or generously fitted system carriers. As a result, unnecessary service routines can be eliminated.
With regard to potential errors in subscribers, the operability of data-receiving subscribers is checked by virtue of the fact that signals are transmitted at a voltage level that is displaced by comparison with the normal transmission of data. Furthermore, at which measure of the displacement of this voltage level at least individual subscribers can no longer receive data is checked, and at least one status map is drawn up in which it is stored with reference to the individual data-receiving subscribers in the form of status data at which displacement of said voltage level at least individual subscribers can no longer receive data (13.3) and/or at which (further) displacement of said voltage level which subscriber or subscribers can, as a last one or ones, still receive data.
This method can be used to check the data-receiving subscribers with regard to the position of their reference-earth potential relative to the position of the reference-earth potential of the transmitted data. Thus, by virtue of the fact that the reference-earth potential of the transmitted data is varied continuously or in steps until it is just no longer possible to receive data, it is possible to determine, taking account of the determined tolerance which was determined assuming that no deviations occur in the reference-earth potential, the extent to which the reference-earth potential of a data-receiving subscriber is displaced with respect to the desired value.
It is advantageously possible by evaluating the status data stored in the map to determine the extent to which a subscriber or the totality of all subscribers of the networked system are in a state of critical potential. It is thus possible thereby to detect a displacement of the reference-earth potential of individual subscribers in a networked system at an early stage, that is to say as early as when the displacement has not yet had the effect that this subscriber can no longer communicate with other subscribers because owing to reference-earth potential differences the signal voltage levels can no longer be discriminated with respect to the threshold values at the receiving end.
In still another embodiment of the present invention, with regard to potential errors in subscribers, the operability of data-transmitting subscribers is checked by virtue of the fact that signals are transmitted by at least one data-transmitting subscriber and, furthermore, to what extent the level of the received signals deviates from the desired value of the signal level in the case of normal transmission of data is checked, and at least one status map is drawn up in which a measure of the deviation determined is stored with reference to the individual data-transmitting subscribers.
This method can be used to check the data-transmitting subscribers with regard to the position of their reference-earth potential relative to the position of the reference-earth potential of the receiving data. Thus, by virtue of the fact that a reception-discriminant reference-earth potential, for example the voltage level, monitored for being overshot or undershot by the data signal, is varied continuously or in steps in a receiving subscriber until it is just no longer possible to receive data, it is possible, taking account of the tolerance determined in the case of absent deviations in the reference-earth potential to determine the extent to which the reference-earth potential of the data-transmitting subscriber is displaced with respect to its desired value. It is advantageously possible by evaluating the status data stored in the map to determine the extent to which a subscriber or the totality of all subscribers of the networked system are in a state of critical potential.
In still another embodiment according to the invention, the signals are transmitted by at least one subscriber of the networked system at a signal level displaced by comparison with the normal transmission of data.
As a result, it is advantageously possible, on the one hand, to minimize the outlay on hardware by virtue of the fact that, for example, only one subscriber of the networked system also takes over this function. Moreover, it is also possible to determine suitable testing times in a flexible way. Such checking can be initiated, for example, whenever it is determined on the basis of the operating conditions of the network that the bus is instantaneously not being used to capacity. This checking cannot then cause interference in the data bus during operation.
In yet another embodiment according to the invention, the checking is carried out by at least one data-receiving subscriber.
As a result, it is advantageously possible, on the one hand, to minimize the outlay on hardware by virtue of the fact that, for example, only one subscriber of the networked system also takes over this function. Moreover, it is also possible to determine suitable testing times in a flexible way. Such checking can be initiated, for example, whenever it is determined on the basis of the operating conditions of the network that the bus is instantaneously not being used to capacity. This checking cannot then cause interference in the data bus during operation. Moreover, checking carried out by a subscriber which receives data influences only the operation of this one subscriber. The operation of the rest of the network is not affected thereby.
In an embodiment of the invention, the smallest measure of the margin of error among individual subscribers is obtained with respect to the at least one criterion from the status data, and the relevant subscriber is marked correspondingly in the status map.
It is possible thereby to detect during the normal system operation, but in any case on the occasion of maintenance of the system carrier, that is to say at the inspection intervals thereof, to detect whether and, if appropriate, which of the system subscribers had or has in the system operation the smallest and, possibly, no longer adequate margin of error with regard to the at least one criterion and, if appropriate, requires a preventative measure so that the availability of the system continues to be reliably provided and the possibility of its emergency operation is reliably provided at any time. It is also advantageously possible by appropriate evaluation of the data stored in the status map to detect whether, for example, a very specific grouping of subscribers is in a critically small margin or error of communication, for example in the case of the presence of potential errors, for example in subscribers of a power supply cluster.
In the case in which a subscriber already has a communication fault because of a no longer adequate margin of error in the at least one criterion, information on the defective subscriber is obtained directly, and the cause of the fault active in it can be verified without any problem from the status map.
In a further embodiment of the invention, the method is carried out on the occasion of the normal commissioning and/or normal decommissioning of the system carrier.
As a result of this measure, it is advantageously possible for an early warning to be triggered as early as during the commissioning of the system carrier, should it be necessary to expect operation which is close to defective, or it is possible to retain the most recent/last state before the occurrence of a system status close to defective on the occasion of a further commissioning. While the first favours security, the second can substantially alleviate servicing the system.
According to another embodiment of the invention, the method is repeatedly carried out in the course of each operation of the system. It is thereby advantageously possible for sporadically occurring irregularities and shrinkage of the margin of error to be detected statistically even during network operation and stored in data form in the status map.
According to an even further embodiment of the invention, a rise time measure, an overshoot measure or a settling time measure of a data signal is discriminated or tested or measured during or after a change in status thereof. Deviations (gradual) from the norm outside permissible tolerances in the case of individual subscribers in the networked system are thus detected early, i.e., already in a stage in which the normal communication within the overall system is not yet disturbed. This is very important, since, for example, once they are strongly expressed reflection-induced communication disturbances can necessarily be diagnosed only expensively.
In a development or an embodiment according to the invention, a reference-earth potential of individual subscribers in the networked system is discriminated or tested or measured. As a result, a (gradual) displacement of the reference-earth potential of individual subscribers in the networked system is detected early, that is to say as early as at a stage in which the displacement of the reference-earth potential of a subscriber has not yet had, or is not sufficient to have the effect that normal communication within the entire system or of this subscriber with one or more other subscriber(s) has been disturbed or become impossible. This is an important feature in ensuring reliable possibilities, that is to say single-wire ones, of emergency operation.
In accordance with a further embodiment of the invention, discriminating or testing or measuring of the reference-earth potential of individual subscribers in the networked system is performed by detecting at least one recessive or dominant signal level in individual subscribers.
This development of the method is useful in a particularly advantageous way when the subscribers in the system in any case contain discriminating means, testing means or measuring means for level values. It is then advantageously possible to minimize the outlay on hardware by virtue of the fact, for example, that it is possible to dispense with means for influencing the signal level at the transmitting end. In this case, the advantages multiply via increasing resolution of the discriminating means, testing means or measuring means for level values, which are also included in the subscribers in the system. Such means can, for example, be components of the receiver part of the transceiver of subscribers (compare WO97/36399, WO97/36398), or else can be assigned to other A/D converting means as a component of a circuit which also includes the transceiver (compare PCT/EP97/01534).
The determination of suitable testing times can be very flexible. By virtue of the fact that the discriminating function, testing function or measuring function can be integrated into the software for operating the networked system, this function can advantageously be used in the course of normal communication operation in the network. At the same time, it can also be initiated when it is determined on the basis of the operating conditions of the system that the bus-type network thereof is instantaneously not being used to capacity. It is then impossible, in any case, for there to be disturbances or flowing down of the data throughput during operation of the bus-type network.
In an even further embodiment of the present invention, discriminating or testing or measuring the at least one recessive or dominant signal level is performed by sampling, by data signal concatenation, the potential on the at least one bus wire within a sampling time which is shorter than a bus bit time of the data signals, that is to say analogous in terms of time to detecting dominant signal levels in accordance with WO97/36399, as FIGS. 25 and 26 there, or in accordance with WO97/36398, as FIGS. 40 and 41 there.
For example, the (in practice) never completely suppressible overshooting of the data signal after level status transitions on the at least one bus wire is thereby suppressed from discriminating, testing or measuring, as a result of which erroneous assessments are excluded.
In an advantageous way, reference-earth potential displacements can thus be detected in the course of normal system operation, it being possible within the scope of the software for operating the networked system to assign in each case to at least one other subscriber the role of a xe2x80x9cmeasurement witnessxe2x80x9d with respect to the verification of the offset, which can be determined during load changing, of the at least one recessive signal level.
In accordance with another embodiment of the invention, a (gradual) displacement of the reference-earth potential can be determined in the case of at least one subscriber during receiving operation thereof by virtue of the fact that a discrimination or measurement is performed in this subscriber of at least one dominant source level fed onto at least one line of the bus-type network, the respectively fed dominant source level being offset with respect to the normal dominant signal level in a respectively predetermined way, and the respective offset being stored in the form of status data in the status map as a function of the discrimination result or measurement result obtained in the receiving subscriber.
In this development, it is possible, for example, to make advantageous use of level discriminators which are also components of receiver parts of the subscribers in the system. Discriminating or measuring can thus be reduced, for example, to checking for which offset of the at least one dominant source level individual subscribers are no longer able to receive data or can receive data again. Consequently, data stored in the status map represent offset values, assigned to the individual receiving subscribers, of said at least one dominant level.
Thus, it is possible by means of this method to check the data-receiving subscribers with respect to the position of their reference-earth potential relative to the position of the reference-earth potential of the subscriber respectively transmitting data. By virtue of the fact that the reference-earth potential of the data-transmitting subscriber is varied continuously or in steps until it is just no longer possible to receive data or until it is just possible to receive data again, it is possible, taking account of the permissible tolerance of the dominant signal level in the bus-type network (which has been determined assuming that no offsets are present in the reference-earth potential in the case of individual subscribers), to determine the extent to which the reference-earth potential of a receiving subscriber is displaced, specifically under all operating conditions in the case of reception, that is to say both in the quiescent state and under operating conditions or test load conditions.
According to another embodiment of the invention, it is possible for a (gradual) displacement of the reference-earth potential to be detected in the case of at least one subscriber during transmitting operation thereof by virtue of the fact that a discrimination or measurement is performed of at least one dominant signal level fed onto at least one line of the bus-type network by this subscriber by virtue of the fact that a reception-discriminant reference level is offset in a respectively predetermined way in the case of or in at least one receiving subscriber, and the respective offset is stored in the form of status data in the status map as a function of the discrimination result or measurement result obtained in the receiving subscriber.
It is advantageously possible in the case of this development, as well, to make use of level discriminators which are also components of subscribers. Discriminating or measuring can thus be reduced, for example, to checking for which offset of their reception-discriminant reference level individual subscribers can still receive data. Consequently, data stored in the status map represent offset values, assigned to the transmitting subscriber, of said at least one reception-discriminant reference level.
According to yet another embodiment of the invention, discriminating or testing or measuring or checking with respect to a specific subscriber is undertaken in each case by at least two other subscribers in the network (witness function).
Within the scope of the software for operating the networked system, at least one other subscriber is in this case assigned the role of a xe2x80x9cmeasurement witnessxe2x80x9d for verifying a determined signal criterion or potential offset of an individual subscriber. It is possible by means of this measure for discrimination errors, testing errors and measurement errors, in particular owing to influences from the system carrier, to be reduced, and for the detection of statistically occurring errors to be enhanced.
In still another embodiment of the invention, discriminating is or testing or measuring or checking with respect to a specific subscriber is undertaken identically with respect to at least one further comparison subscriber as well, and a plausibility selection is made in the status map with respect to the result.
In this case, the identical comparative measurement can be undertaken, for example, in an alternative fashion, in an alternating fashion or for the purpose of master-slave processing. Within the scope of the software for operating the networked system, the status map is in this case assigned the role of an xe2x80x9cacceptorxe2x80x9d or xe2x80x9capproverxe2x80x9d with respect to a plausible selection from a plurality of discriminating results, testing results, measuring results or checking results.
By virtue of the fact that, for example, discriminating or measuring is undertaken by different receiving subscribers, it is possible to evaluate on the basis of a plausibility confirmation supported by a witness or acceptor whether the change in a signal criterion, for example a displacement of a reference-earth potential, is caused at a data-receiving subscriber or at a data-transmitting subscriber. If, for example, a reference-earth potential displacement is determined by a plurality of data-receiving subscribers, it is possible to conclude under specific preconditions that the determined potential displacement is present, rather, at the data-transmitting subscriber. By virtue of the fact that data relating to the relative position of a plurality of data-receiving subscribers are exchanged, it is thus also possible to detect and evaluate in a particularly simple way where a disturbance has been caused in the network topology.
In a development of an embodiment according to the invention, data signals having at least one dominant source level offset with respect to the normal dominant level are transmitted into the bus-type network by at least one subscriber of the networked system.
By virtue of the fact that in the case of this development of the method, for example, only one subscriber needs to be equipped for generating offset dominant source levels, it is also possible thereby to achieve an advantageous minimization of the outlay on hardware.
According to an even further embodiment of the invention, it is possible to make use of level discriminators which are also components of receiver parts of the subscribers in the system, with the result that there is no need to make an outlay for special level discriminators or, for example, A/D conversion means. This serves to minimize the outlay on hardware.
According to another embodiment of the invention, the discriminating or testing or checking or measuring is performed under network-wide defined quiescent conditions and/or operating conditions or test load conditions of individual subscribers.
If consumers with current-supplying subscribers are subjected to quiescent conditions and load current conditions or test load conditions, it is possible, by evaluating the status data stored in the map, to detect advantageously in a simple way the extent to which individual subscribers are in a critical state as a function of supply with regard to their reliable ability to communicate.
In accordance with yet another embodiment of the invention, the status map is operated in at least one subscriber permanently belonging to the networked system. As a result, the status data characterizing the system status with regard to the tested subscribers with respect to the at least one criterion are advantageously available at anytime in the system. On the other hand, discriminating or testing or checking or measuring can thus also be performed cyclically, for example, during the operation of the networked system.
According to another embodiment of the invention, the status map is stored in a non-volatile fashion. All the data in the status map are advantageously protected thereby against loss in the case of power failure or decommissioning of the system or system carrier. Moreover, it is thus possible to access the status data at any timexe2x80x94for example at specific event intervals.
In another embodiment according to the invention, the status map is updated continuously, older parts of the contents being overwritten with newer parts of the contents. It is advantageously ensured as a result that the status map always has the most up-to-date status data ready.
According to another embodiment of the invention, (the) status data characterizing at least one earlier system status are held at least temporarily in the status map together with (the) status data, characterizing the current system status. In an advantageous way this measure renders possible event-dependent evaluations which have recourse to the prehistory of the margin of error. For example, it thus becomes possible to evaluate impairments which occur only occasionally or in a fashion statistically distributed over time.
According to even a further embodiment of the invention, at least one trend variable is derived with respect to the tendential development of a deviation or of a measure of the margin of error of the at least one signal criterion in the system from status data which are at least temporarily present in the status map and characterize the current and at least one earlier system status. The at least one trend variable advantageously provides a direct measure for the degree of urgency of an anticipatory measure for the purpose of safeguarding the availability of the system. Apart from that, this development of the method renders it possible to assess the network quality of the system over time both with respect to appropriate individual criteria and overall.
According to still a further embodiment of the invention, the derivation of the trend variable is undertaken by means of the software for operating the networked system. This results in the advantage that the trend variable can be determined in a particularly simple way outside the status map as well, for example in a subscriber of the networked system, and that the network communication can be transferred in a subordinate fashion into the status map.
According to yet a further embodiment of the invention, the deviation or the measure of the margin of error and/or the at least one trend variable is/are held in the status map in a non-volatile fashion. As a result of this measure, it is advantageously possible, for example after a system failure has occurred, for the cause thereof still to be reconstructed. On the other hand, it is thus possible after a subscriber failure or system failure to find information in a simple and reliable way for the purpose of quickly restoring the system again. The permanent possibility of fetching such trend data also renders possible in a cost-effective way simple and informative displays of critical communicative operating conditions of individual subscribers of the system directly on the system carrier.
According to another embodiment of the invention, the discriminating or testing or checking or measuring and at least one of the operations of collecting, conditioning, arranging and evaluating status data in the status map are undertaken by an online diagnostic program which is integrated with or into the software for operating the networked system and, with regard to its execution, is subordinate to the normal network operation and to that extent runs in a latent fashion.
By virtue of the fact that to this extent at least a part of the care and/or management of the status map is integrated into the software for operating the networked system, discriminating, testing or checking or measuring can, for example, advantageously be initiated as often as permitted by the instantaneous communication requirements up to using the bus-type network to capacity. As a result, on the one hand disturbances or retardations of the data throughput during operation of the bus-type network are excluded, and on the other hand a high degree of updating of status data available from the status map is ensured by virtue of the fact that light-load phases of the communication in the network can advantageously be utilized for updating and caring for the status map.
According to another embodiment of the invention, there is connected as a further subscriber to the networked system a test instrument which reads out at least parts of the status map. It is possible as a result to carry out routine checks in an advantageous way on the occasion of inspections of the system carrier by means of test instruments which are particularly simple and easy to manipulate. On the one hand, it is possible thereby to use the data characterizing the system status with regard to the tested subscribers with respect to the at least one criterion to condition corresponding trend data outside the networked system as well. On the other hand, it is possible thereby advantageously to detect in a simple way during routine inspections of the system carrier when the communicative operating conditions of a subscriber worsen or have worsened critically and call for prevention.
In another embodiment according to the invention, at least one subscriber permanently belonging to the system is fitted with display devices and/or signalling devices, and given overshooting of an upper limiting value for the measure of the deviation or the trend variable, or given undershooting of a lower limiting value for the at least one measure of the margin of error, this status is indicated or signalled by the subscriber. It is possible by means of this measure, for example, for a user of the system carrier to be made aware without damage of an inspection requirement even during operation of this system carrier.
According to another embodiment of the invention, parts of the status data stored in the status map and/or the measure of the deviation or a measure of the margin of error of the system or of a subscriber, and/or the at least one trend variable is/are written into an electronic authorization means for using and/or for commissioning the system carrier. According to this development, it is possible in an advantageous way for corresponding data to be written into or written back to an electronic xe2x80x9cauthorization keyxe2x80x9d of a system carrier when the latter is commissioned or before it is decommissioned. This opens up novel security functions and can, in addition, support the rationalization of the inspection operation for appropriately equipped system carriers.
According to even a further embodiment of the invention, after the commissioning and initialization of the networked system a first discrimination or testing or checking or measuring is undertaken immediately, and in this process a smaller number of subscribers and/or a smaller number of signal criteria are selectively subjected to being discriminated or tested or measured than in the case of the subsequent further conduct of the method. It is possible by means of this measure, for example, to test the communicative ability and operability of a subscriber bearing a status map in a particularly time-saving fashion immediately after initialization.
According to another embodiment of the invention, at least two status maps are provided and used in two different subscribers of the system. It is possible by means of this measure, inter alia, to achieve a high degree of security against loss of information.
According to even a further embodiment of the invention, provided in the system are two different status maps which are changed and/or processed and/or read out independently of one another in each case for different test methods and/or test programs. It is possible by means of this measure, for example, for the availability of specific subscribers to be safeguarded separately, and for specific status data to be protected against unauthorized access.
According to still a further embodiment of the invention, in the course of discriminating or testing or checking or measuring, at least individual subscribers respectively supply operating currents to at least one electrical consumer external to the subscriber. It is possible by means of this measure for potential errors or EMC interference, caused inside the system, of individual subscribers to be detected and located particularly effectively.
In accordance with another embodiment of the invention, a test load which can be driven via the bus-type network for the purpose of providing current is provided at least in individual subscribers of the system, and said load is driven in the course of discriminating or testing or checking or measuring. It is possible by means of this measure for potential errors or EMC interference caused by the subscriber itself to be detected particularly effectively. Furthermore, it is possible by means of this measure, for example, to test the overload-carrying capacity of the power supply terminals or of the corresponding supply lines of individual subscribers.
If subscribers with an internal test load are subjected, for example, alternately or in an alternating fashion to different quiescent conditions and load current conditions or test load conditions, it is possible given knowledge of the network topology of the system to reach a PARTICULARLY EFFECTIVE conclusion on the location (of the production) of a fault on the system carrier which, although it does influence the system, has a cause outside the system, doing so, for example, with the aid of reference-earth potential displacements of different subscribers or with the aid of coupling and/or electromagnetic signal impairments in the case of different subscribers by evaluating corresponding status data from the at least one status map.
In accordance with another embodiment of the invention, the external operating voltage, which can be detected inside subscribers, or a voltage derived therefrom is also discriminated or tested or checked or measured, and with respect to this status data are generated and stored and/or processed and/or evaluated in the at least one status map. It is possible by means of this measure also for potential errors or EMC interference, caused inside the system, of individual subscribers to be effectively detected and/or located. Furthermore, it is possible by means of this measure, for example, to test the overload-carrying capacity of the power supply terminals or of the corresponding supply lines of individual subscribers.
According to another embodiment of the invention, at least one status map has a subscriber identification section, a status data stack and a data processing section.
According to yet another embodiment of the invention, the identification section comprises a table via which each system identifier and/or subscriber in the system is assigned as required its topological identification or a topological identifier within the network.
According to another embodiment of the invention, the data stack comprises a multiplicity, corresponding to the number of signal criteria to be tested, of register stacks in which or through which are routed status data in accordance with their aging progress.
According to another embodiment of the invention, the data processing section has at least one area for data selection and one area for data processing, it being the case that status data are selected and/or reorganized in the former at least in terms of minimum and maximum values, and data indicative of change are generated in the latter from status data as a function of their age and/or temporal occurrence.
Advantages of the four last named developments relating to the method are shown in the description of the figures.
In accordance with an even further embodiment of the invention, the method is carried out in the case of a transport means. This produces a high availability and security against accidents caused by system failure.
The drawing first illustrates some hardware details which subscribers can have, by way of example, in order to permit specific method steps to be carried out. Without this representation laying claim to completeness or signifying any limitation of the invention, the exemplary case of a reference-earth potential test is taken up here. Within the scope of the invention, it is possible for this purpose and for testing signal criteria which are not associated with potential for subscribers nevertheless also to provide quite other means (The hardware details shown are taken partly from WO97/36399, for which reason the description is kept short. For further details, reference may be made to WO97/36399 and, regarding aspects of the circuitry, to DE19611944, WO97/36398 and PCT/EP97/01534).